Semantic difficulties arise when hypertrophic obstructive cardiomyopathy is seen without obstruction and with congestive failure, and also when congestive cardiomyopathy is seen with gross hypertrophy but without heart failure. Retention of a small left ventricular cavity and a normal ejection fraction characterizes hypertrophic cardiomyopathy at all stages of the disorder. Congestive cardiomyopathy is recognized by the presence of a dilated left ventricular cavity and reduced ejection fraction regardless of the amount of hypertrophy and the presence or not of heart failure.
Longevity in congestive cardiomyopathy seems to be promoted when hypertrophy is great relative to the amount of pump failure as measured by increase in cavity size. Conversely, death in hypertrophic cardiomyopathy is most likely when hypertrophy is greatest at a time when outflow tract obstruction has been replaced by inflow restriction caused by diminishing ventricular distensibility. Hypertrophy is thus beneficial and compensatory in congestive cardiomyopathy, whereas it may be the primary disorder and eventual cause of death in hypertrophic cardiomyopathy.
Reasons are given for believing that hypertension may have been the original cause of left ventricular dilatation in some case of congestive cardiomyopathy in which loss of stroke output thenceforward is followed by normotension. Development of severe hypertension in these patients after recovery from a prolonged period of left ventricular failure with normotension lends weight to this hypothesis.
No fault has been found in the large or small coronary arteries in either hypertrophic cardiomyopathy or congestive cardiomyopathy when they have been examined in life by selective coronary angiography, or by histological methods in biopsy or post-mortem material. Coronary blood supply may be a limiting factor in the compensatory hypertrophy of congestive cardiomyopathy, and the ability to hypertrophy may explain the better prognosis of some patients. In hypertrophic cardiomyopathy excessive metabolic demand may not be met, and inadequacy of blood flow may contribute both to sudden death and to progressive replacement fibrosis in this disease.
Histochemical and ultrastructural methods have failed to show any fundamental differences between hypertrophic cardiomyopathy and congestive cardiomyopathy, whereas conventional histology permits recognition of hypertrophic cardiomyopathy and distinction both from congestive cardiomyopathy and from `normal' secondary hypertrophy in organic aortic stenosis.
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